They will and do something called acceptance testing, which is nothing but testing in prod.

Not quite. Nobody acceptance tests an airliner on a passenger flight. If we acceptance test a medical diagnostics device, we don't run the test the doctor later relies on with the DUT.

This is a common misconception about testing in prod. It’s not about the logic. To quote the article: “Once you deploy, you aren’t testing code anymore, you’re testing systems.”

I don't quite get the objection. For me, "testing in prod" is "we observe the actual running system, with production traffic and users directly interacting with it and its results being live". That's not quite what "acceptance testing" in the mentioned-above domains is. If you have an acceptance testing stage, prod follows it.

I think the argument breaks down when you have systems as opposed to objects.

You can't acceptance test "Google's search", because at a minimum doing so would require some kind of reverse proxy that is itself part of the system and can't be acceptance tested without...and turtles etc.

Another way of putting this might be that there isn't a good way to acceptance test "airplane manufacturing companies". There isn't a set of acceptance tests you can run to ensure that Boeing is performing to spec before having it build real airplanes.

Maybe, I don't feel particularly strongly either way about if it can be applied to the kind of large services you are thinking of. But also wasn't really the point of my comment, I merely rejected the claim that acceptance testing in fields where it is done is the same as testing in prod.

Perhaps the closest analogy would be deploying to a limited subset of users on closely monitored boxes.

It's clearly not perfect though, except perhaps if the test aircraft turned itself into a crater on the runway, there is very little one aircraft can do to effect the function of all others.

In software it's hard to get this kind of guarantee, a new delete with a missing where clause in your canary environment is going to take some time to clean up after (assuming you have backups etc).

Acceptance tests of aircraft are done by the pilots sent by the owner, not the factory. They do some flying and follow a checklist which is again unique to the company. It's like sending out your software for evaluation, which is in production and its evaluated by clients. You don't send testing/staging software for evaluation by clients.

You absolutely can and should test in prod in these cases.

We call that FDA testing

FDA does not test anything.

I'm not sure how this is a useful observation. Units don't test anything, but it's still called Unit Testing.

They test my patience!